Rescuegrass (Bromus catharticus) is a monocot weed in the Poaceae family. In Argentina this weed first evolved resistance to Group G/9 herbicides in 2017 and infests Fallow, Wheat, and Winter barley. Group G/9 herbicides are known as EPSP synthase inhibitors (Inhibition of EPSP synthase). Research has shown that these particular biotypes are resistant to glyphosate and they may be cross-resistant to other Group G/9 herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

Greenhouse trials comparing a known susceptible Rescuegrass biotype with this Rescuegrass biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on Group G/9 resistant Rescuegrass have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group G/9 resistant Rescuegrass from Argentina please update the database.

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Argentina have been instrumental in providing you this information. Particular thanks is given to Marcos Yanniccari for providing detailed information.

Three field experiments were conducted in New Zealand. In the first trial (1995), Fenoxaprop P-ethyl [fenoxaprop-P], a wild oat (Avena sativa) herbicide, was applied to five grass species (Lolium perenne cv. Grasslands Nui, L. multiflorum cv. Concord, Bromus willdenowii [B. catharticus] cv. Grasslands Matua, Bromus stamineus cv. Grasslands Gala and Phalaris aquatica cv. Grasslands Maru). L. perenne was tolerant to 37 g/ha, but there was a trend for a reduction in seed yield at 75 g/ha. The two Bromus species had good tolerance, but P. aquatica seed yields were reduced by 80%. In the second trial (1996-97), fenoxaprop P-ethyl applied at 56 g/ha had no significant effect on seed yield of perennial and hybrid ryegrass cultivars (Yatsyn and Grasslands Impact, respectively). However, there was a trend for 75 g/ha to reduce seed yield in the perennial ryegrass. In the third experiment (1997) involving L. perenne cv. Verdette, wild oats were very competitive, reducing seed yields from 2600 kg/ha (best herbicide treatment) to 660 kg/ha in the untreated control. Excellent wild oat control was achieved with fenoxaprop P-ethyl at rates of 45 g/ha in August and 56 g/ha in September..